Recently, the general trends in designing power converters are toward high efficiency and high density. The high efficiency power converter can reduce the power loss and achieve the power-saving purpose. The high density power converter can reduce the overall volume of the electronic product and meet the requirements of small size and light weightiness.
Generally, a power converter comprises a bridge circuit for rectification. The bridge circuit comprises at least one high-voltage-side switching element and at least one low-voltage-side switching element. For example, a three-phase bridge circuit of a three-phase power converter comprises three high-voltage-side switching elements and three low-voltage-side switching elements. The high-voltage-side switching elements are connected with the corresponding low-voltage-side switching elements in series. Each of the high-voltage-side switching elements and the low-voltage-side switching elements comprises a semiconductor switch and a diode, which are connected with each other in parallel. For example, the semiconductor switch is an insulated-gate bipolar transistor (IGBT). By alternately turning on and turning off the semiconductor switch, the bridge circuit can rectify the input power. When the semiconductor switch is turned off, the diode allows the current to continuously flow.
A conventional method of fabricating the bridge circuit of the power converter will be illustrated as follows. Firstly, the semiconductor switches and the diodes of the high-voltage-side switching elements and the semiconductor switches and the diodes of the low-voltage-side switching elements are disposed on a substrate. Then, the semiconductor switches and the diodes of the high-voltage-side switching elements and the semiconductor switches and the diodes of the low-voltage-side switching elements are connected with each other and/or connected with an external component by a wire-bonded technology (e.g. through aluminum wires or copper wires). Afterwards, the above structure is packaged by an encapsulation material.
However, since the high-voltage-side switching elements and the low-voltage-side switching elements are connected with each other by the wire-bonded technology, some drawbacks occur. For example, the long wires for connecting the high-voltage-side switching elements and the low-voltage-side switching elements may increase the parasitic inductance between the wires and the substrate. Under this circumstance, the switching efficiency of the high-voltage-side switching elements and the low-voltage-side switching elements will be adversely affected. Moreover, since the long wire has a large impedance value, the power conversion efficiency is impaired. Moreover, the side of the substrate for wire-bonding the high-voltage-side switching elements and the low-voltage-side switching elements cannot be equipped with any heat dissipation device. Since the substrate is only able to dissipate away heat in a single direction, the heat dissipating efficiency is insufficient. Moreover, since it is necessary to retain a wire-bonded area on the substrate, the space utilization of the substrate is limited. Under this circumstance, it is difficult to increase the power density. Moreover, the high-voltage-side switching elements and the low-voltage-side switching elements of the bridge circuit are packaged after being mounted on the substrate. After the bridge circuit is fabricated, if one component of the high-voltage-side switching element or the low-voltage-side switching element has malfunction, the damaged component cannot be replaced with a new one. Under this circumstance, the whole bridge circuit cannot be used again.
Therefore, there is a need of providing an improved power module so as to overcome the above drawbacks.